Arc tube mounting



July 29, 1958 K. GOTTSCHALK ARC TUBE MOUNTING Filed Aug. 50, 1956 lnvesn tov: KLaus GotlrschaLl b 1% 8 His A'TdTOVne ARC TUBE MOUNTING Klaus Gottschalk, South Euclid, Ohio, assignor to General Electric Company, a corporation of New York Application August 30, 1956, Serial No. 607,096

4 Claims. Cl. 313-25 This invention relates to electric lamps of the highpressure mercury vapor discharge type having an arc tube mounted in a vitreous outer envelope or jacket. The invention is more particularly concerned with the mounting of the arc tube in the jacket.

A form of commercially available high-pressure mercury vapor discharge lamp comprises a quartz arc tube enclosed in a vitreous outer envelope or jacket provided with a screw base at one end. The are tube contains a quantity of mercury along with a starting gas and is provided with thermionic electrodes containing a core of material of high electron emissivity. The space between the arc tube and the outer envelope or jacket may be either evacuated or filled with an inert gas such as nitrogen. There is also provided within this space a current'limiting resistor which is connected between an auxiliary starting electrode at one end of the are tube and the main electrode at the other end.

It is necessary to maintain the arc tube centrally located within the outer envelope and to provide connections from its electrodes to the screw base terminals. In the past, this has generally been accomplished by means of a frame or harp comprising a pair of support nods fastened at one end to the main inleads through the stem of the outer jacket, and supported at the other end by spring members bearing against the glass envelope, the arc tube being held in place relative to the support rods by transverse members or clamps fastened to the rods and engaging the ends of the arc tube or its seals.

In copending application Serial No. 607,004 of Ernest C. Martt et al., filed of even date herewith, entitled Arc Tube Mount, and assigned to the same assignee' as the present invention, there is disclosed a mounting for an arc tube in a jacketed high-pressure discharge lamp which provides instead support wires or dummy leads secured in the pinch seals and serving as integral mount supports. The dummy leads at the base end of the arc tube may be fastened directly to the main inleads through the stem tube of the outer jacket, whereas those leads at the outer end of the arc tube may have fastened thereto spring members bearing against the outer end of the jacket.

It has been found in the manufacture of high-pressure discharge lamps with are tubes having integral mount supports consisting of dummy leads embedded near the corners of pinch seals, that there is a tendency for the quartz to crack in the vicinity of the dummy leads dur' ing handling and shipping or after repeated operation of the lamp. The principal object of the invention is to provide a solution to this problem.

In accordance with the invention, a solution to the problem of cracking of the quartz pinch seals in the vicinity of the dummy leads resides in causing the dummy leads to enter the seals through conical or funnel-like openings at their outer ends and in embedding the dummy leads in the quartz between the folded walls of the seals beyond the vertices of the conical openings.

tates Ptnt For further objects and advantages and for a detailed description of the invention, attention is now directed to the following description and accompanying drawing illustrating a preferred embodiment and the manner in which it is made. The features of the invention believed to be novel will be more particularly pointed out in the appended claims.

In the drawings:

Fig. 1 is a front elevation view of a high-pressure mercury vapor lamp embodying the invention with the front portion of the outer jacket cut away to expose the arc tube and its seal and mounting structure.

Fig. 2 is a pictorial view illustrating a pinch seal with integral mount supports and its manner of manufac- .ture.

Referring to the drawing and more particularly to Fig. 1, there is shown a high-pressure mercury vapor lamp 1 comprising an outer vitreous envelope or jacket 2 of generally tubular form modified 'by a central bulbous portion 3 to achieve cooler operation of the jacket in the immediate vicinity of the arc tube. The jacket is provided at its lower end with a re-entrant stem 4 having a press 5 through which extend main in-lead wires 6, 7 connected at their outer ends to the contacts of the usual screw type base 8, namely the threaded shell 9 and the insulated center contact 11.

The inner arc tube 12 is made of quartz and has sealed therein at opposite ends a pair of main discharge supporting electrodes 13, 14 supported on in-leads 15, 16 which constitute the arc tube terminals. As illustrated, each main electrode comprises a core portion 17 which may be a prolongation of the inner end of the inlead made of a suitable refractory metal such as tungstem or molybdenum, and surrounded by a tungsten wire helix 18. A small elongated piece or sliver 19 of thorium metal inserted between the core and the helix serves to reduce the cathode drop at the electrodes during operation. An auxiliary starting electrode 21 is provided at the base end of the arc tube adjacent the main electrode 13 and supported on an inlead 22.

Current inleads 15, 16 and 22 as illustrated each comprise a central molybdenum foil section 23 which is bonded to the quartz in pinch seal 24 or 25, an outer molybdenum wire section projecting outwardly of the seal, and a tungsten wire section projecting inwardly into the arc tube and forming, in the case of main electrodes 13 and 14, the core portion 17 of the electrodes. The foil'sections may have a thickness of approximately .0008 inch and a width of approximately .12 inch. Alternatively, the current inleads may be made of a single piece of molybdenum wire having a foliated central portion in accordance with the teachings of Patent 2,667,595, Noel et al., Ribbon Lead Construction, issued January 26, 1954, to the assignee of this application.

The arc tube has a filling of an ionizable medium consisting of a supply of mercury in sufi'icient quantity to be completely vaporized with a pressure of the order of one-half to several atmospheres during operation of the lamp, and in addition a small quantity of an inert gas such as argon at a low pressure, for instance 25 mm. pressure, to facilitate starting and warm-up of the tube.

The pinched end portions 24, 25 of the arc tube form wide seals extending the full diameter of the tube. The pinch seals are made by flattening or compressing the circular ends of the arc tube Without prior necking down to a smaller diameter. The width of the seals then corresponds to approximately 11'/ 2 times the diameter of the arc tube; in practice it is usually less than the figure obtained by this relationship due to slight necking down of the quartz end by surface tension while heated to a plastic temperature during the sealingoperation, but is at least as 3 great as the tube diameter. Thus in a 400-watt lamp designated H-400-E1 wherein the arc tube has an outside diameter of approximately 22 mm. and an inside diameter of approximately mm., the pinch seal width may be from 25 to mm.

The are tube is supported in the outer jacket by means of integral support wires or dummy leads 26, 27 in the lower seal 24 at the base end of the lamp and 28, 29 in the upper seal 25 at the outer end of the lamp. In the illustrated embodiment, the dummy leads do not extend into the interior of the arc tube and a hermetic seal is therefore not necessary; it suffices that the dummy leads be wedged within the pinch seals and mechanically locked in place. Since the dummy leads are not required to be hermetically sealed, they need not be foliated and may be made of round Wire, for instance molybdenum or other suitable refactory metal such as tungsten or tantalum. The inner ends of the dummy leads are preferably expanded in a transverse dimension, for instance by pinching or flattening: the resulting fish-tail form shown at 30 serves to key the lead in the quartz.

Dummy leads 26 to 29 are located near the corners, that is near the outside lateral edges of the pinch seals in which they are embedded. They are thus considerably re moved from the immediate vicinity of the main electrode inleads 15, 16 and the high heat concentrations thereabout. Nevertheless, it has been found that where the dummy leads are embedded directly in the seal, excessive stresses may be set up in the quartz at the outer edge of the seal with a resultant tendency to crack off the outer corners of the seal during handling or shipping or after repeated operation of the lamp.

In accordance with the invention, a solution to this problem resides in the provision of inwardly directed conical or funnel-shaped cavities 31 at the points where the dummy leads penetrate into the folds of the seals formed by fusing together the inner surfaces of the quartz walls of the arc tube. The dummy leads do not engage or contact the quartz except inwardly of the apices of the funnel-like openings, and therefore at points substantially removed from the outer edges of the seal. This feature substantially eliminates the problem of the corners of the pinch seals cracking oif.

Suitable dimensions for the funnel-like openings for the illustrated lamp are as follows: a diameter at the mouth of the opening in the range of the thickness of the seal, for instance 2 to 4 mm.; and an axial length of the opening about equal to or longer than the diameter at the mouth. The dimensions of the conical apertures are not critical and substantial variations from these figures, particularly in the direction of making the apertures larger, are permissible.

The dummy leads 26 to 29 provide the entire support for the arc tube within the outer jacket. Dummy leads 26 and 27 are fastened, for instance by welding, to the laterally turned ends of main inleads 6 and 7 projecting inwardly from the stem tube of the jacket. Dummy lead 26 serves also in part as a current conductor through flexible strap or wire 32 which connects it to main electrode inlead 15. Lead wire 6 is connected by a flexible strap or wire 33 to main electrode inlead 16 at the outer end of the arc tube, and is also connected through series resistor 34 to starting electrode inlead 22 at the base end of the arc tube. Dummy leads 28, 29 at the upper end of the arc tube are fastened to a transverse brace member 35 to which are attached spring fingers 36 bearing against the outer tubular end of the jacket. A heat reflector disc 37 is mounted transversely to the axis of the envelope immediately above the laterally turned ends of main lead wires 6, 7. The disc is welded to lead wire 6 and is slotted at 38 about the region of the laterally turned end of main lead wire 7 so as to avoid contact with that lead or the connections thereto.

Fig. 2 illustrates in a fragmentary perspective the manner of forming a pinch seal with integral mount supports and funnel-like openings thereabout in accordance with the invention. The leads required to be embedded in the seal, namely integral mcrnt support 26, inlead 15 for main electrode 13, inlead 22 for auxiliary electrode 21, and integral mount support 27 are supported upright on the upper surface of a cylindrical mount pin 40, their lower ends being received in suitable apertures in the upper surface of the pin. The quartz tube is supported either by an exhaust tubulation projecting laterally and which is subsequently tipped off, as shown at 41 in Fig. l, or by a suitable chuck engaging its body. The tube is held so that its lower surface just clears the top surface of the mount pin, the cylindrical outline of the tube prior to pinching being shown at 12' in Fig. 2.

A pair of pinching jaws 42 and 43 are mounted in opposed positions with respect to the seal assembly on the mount pin and suitable means are provided to advance the jaws simultaneously together in a direction normal to the plane of the pinch seal. The jaws have a concave upper surface 44 to provide a generally hemispherical closure to the arc tube. The shape of the jaw surfaces and the actuating mechanism therefor, along with the burners for heating the quartz tube to plasticity, may be similar to those described in my co-pending application Serial No. 607,005, filed of even date herewith, entitled Quartz Tube Pinch Sea and assigned to the same assignee as the present invention. The resulting seal is thicker at the center along an axial line than at the lateral edges and is thinner, that is, more highly compressed, at the curved inner edge adjacent the arc tube than at the edge. Preferably the jaws are provided with shallow grooves cut across in transverse and axial directions in order to restrict flow of the plastic quartz thereunder at pinching. The grooves are shown at 45 and 46 in jaw 42 and result in transverse ridges 47 and axial ridges 48 in the surfaces of the seal. Both jaws are provided with cavities or cutouts 49 at their lower edges conforming to the funnel-like apertures 31 at the outer edges of the seal through which the integral mount sup ports penetrate into the fold of the seal. When the jaws are closed upon the plastic quartz, the quartz conforms itself to surface of the cavities, thereby producing the desired funnel-like openings.

While the present invention has been described by reference to a specific preferred embodiment of same, the details of construction described are intended as exemplary and not in order to limit the invention thereto except in so far as included in the accompanying claims. In particular, the invention is equally applicable to moditied integral mount constructions wherein the integral mount leads are connected within the seals to the foils of the inleads and serve as current conductors therefor. Such constructions are described and claimed in my copending application Serial No. 607,006, filed of even date herewith, entitled Arc Tube Seal and Mount, and assigned to the same assignee as the present invention.

What is claimed as new and desired to be secured by Letters Patent of the United States is:

l. A vitreous tube having an end sealed by an axially projecting flat pinch seal of width at least substantially as great as the diameter of the tube and having a leadin conductor hermetically sealed therethrough, and support wires embedded in the seal near its lateral edges and projecting through funnel-like openings in its outer edge and forming integral mount supports for the tube.

2. A quartz tube having its ends sealed by axially projecting flat pinch seals of width at least substantially as great as the diameter of the tube and having lcadin couductors with intermediate foil portions hermetically sealed through their central portions, and support wires embedded in the seals near their lateral edges and pre jecting axially through funnel-like openings in their outer edges and forming integral mount supports for the tube within an enclosing envelope.

3. An arc tube for an electric discharge lamp of the jacketed high-pressure type having its ends sealed by axially projecting flat pinch seals of width at least substantially asgreat as the diameter of the tube and having lead-in conductors including intermediate foil portions hermetically sealed through their central portions, and support wires embedded in the seals and projecting axially through funnel-like openings in the outer edges of the seals and forming integral mount supports for the tube within an enclosing envelope, said openings having a diameter at their mouths in the range of the thickness of the seals.

4. An electric discharge lamp of the jacketed highpressure type comprising a vitreous outer envelope enclosing a quartz arc tube, said tube having at each end an axially projecting flat pinch seal of width at least substantially as great as the diameter of the arc tube with a lead-in conductor having an intermediate foil portion hermetically sealed through its central portion, support wires embedded within the seals near their lateral edges and projecting from their outer ends through funnellike openings formed in the outer edges of the seals about the support wires and avoiding engagement between the References Cited in the file of this patent UNITED STATES PATENTS 1,948,261 Francis et a1. Feb. 20, 1934 2,273,450 Rentschler Feb. 17, 1942 2,677,068

Martt Apr. 27, 1954 

